About Sika Sikadur-55 LP IN

Sikadur-55 LP IN is Sika’s answer to a problem every repair engineer in India runs into: a structural crack that needs re-bonding, but a substrate that refuses to dry out. Conventional epoxy resins demand a bone-dry crack and turn milky or fail to cure when moisture is present. This resin is formulated as a low-viscosity, moisture-insensitive injection liquid built on a high-strength epoxy, so it flows readily into fine cracks and still develops full mechanical properties on dry or damp faces. It is engineered for hot and tropical climates, which makes it well suited to Indian site conditions, and it carries an ASTM C881 Type II & IV, Grade 1, Class F declaration.

Once mixed and placed, the resin wets the crack walls, penetrates by capillarity or under injection pressure, and cures shrinkage-free into a hard-but-not-brittle solid. The cured resin measures roughly 70 N/mm² in compression, around 50 N/mm² in both flexure and tension, and bonds to concrete at 10 N/mm² or more after moist curing. In practice that means the repaired member behaves monolithically again, transferring load across the former crack rather than around it. Because it injects cleanly with single-component pumps and pours for horizontal saturation, one product covers both the pressure-injection and gravity-feed routes an applicator typically needs on site.

The technical insight

The engineering value of Sikadur-55 LP IN lies in the pairing of very low viscosity with genuine moisture tolerance. At roughly 250 mPa·s (near water-like flow) the resin exploits capillary action to travel the full depth of a crack rather than bridging only the mouth, which is what separates a real structural repair from a cosmetic surface seal. Cracks as narrow as 0.1 mm can be reached and up to 5 mm injected. The moisture-insensitive chemistry is the second half of the story: most epoxies are displaced by, or refuse to cure against, a water film, so a damp crack has to be dried first, which is rarely practical on a live structure or a water-retaining wall. This resin cures against damp faces and even develops high bond strength in wet cracks, so the crack face need only be free of standing water, not dry. Shrinkage-free hardening means the resin does not pull away from the crack walls as it sets, preserving full contact, and the cured matrix is formulated to be hard but not brittle so it can carry stress across the joint without cracking through itself. The result is a restored load path with adhesion (=10 N/mm² at 14 days) that comfortably exceeds the tensile capacity of the surrounding concrete, so a correctly injected member typically re-cracks in fresh concrete rather than along the repaired line.

Where it is used

• Pressure injection of structural cracks in concrete slabs, columns, beams, walls and foundations
• Gravity-feed or brush saturation of cracks on horizontal surfaces such as floor and roof slabs
• Repair of cracks in damp or wet concrete where drying the substrate is not feasible
• Re-bonding of cracks in water-retaining structures and below-grade elements
• Crack sealing in parking decks and structures exposed to pedestrian and vehicular traffic
• Rehabilitation of cracked concrete in bridges and other infrastructure in hot, tropical climates
• Restoring monolithic load transfer across cracked structural members prior to further strengthening
• Surface treatment of fine cracks in interior and exterior slabs to arrest ingress

Key advantages

• Moisture insensitive, so it bonds and cures on dry or damp crack faces without a separate drying step
• Very low viscosity (~250 mPa·s) that penetrates fine cracks and reaches full crack depth
• Solvent-free formulation, reducing odour and health concerns in enclosed repair areas
• Shrinkage-free hardening keeps the resin in full contact with the crack walls
• High mechanical strength: ~70 N/mm² compressive and ~50 N/mm² tensile
• High bond strength (=10 N/mm² at 14 days) even in wet cracks, per ASTM C882
• Hard but not brittle cured resin that carries stress across the repaired joint
• Injectable with simple single-component pumps and equally suited to gravity feed

Limitations & considerations

• Maximum injectable crack width is 5 mm; wider cracks need a different Sika solution and technical guidance
• Not for use against standing or running water, though damp faces are acceptable
• Ambient and substrate temperatures must sit between +10 °C and +40 °C during application
• Pot life is limited (>60 min for a 100 g mass at +30 °C) and shortens further with larger masses and heat
• Requires proper substrate preparation, thorough crack cleaning and correct 4:1 mixing to achieve rated strengths
• Rigid epoxy repair is unsuitable for moving or actively working cracks, which need a flexible or elastic treatment instead

Selection & best practice

Specifications

Industry use cases

How we position Sika Sikadur-55 LP IN

Sikadur-55 LP IN sits in Sika’s crack-repair range as the low-viscosity, moisture-tolerant injection resin. Within the same Sika family, pair it with Sikadur-31 IN epoxy mortar to surface-seal the crack line and stop resin loss during injection, and use Sikaflex sealant to form pouring barriers on horizontal work; for actively moving joints that a rigid epoxy cannot serve, move to a flexible Sikaflex sealant instead. Where a specifier prefers a Fosroc-based system, or already standardises on Fosroc for a project, the closest counterpart from our other brands is Fosroc Nitofill LV. We supply and apply both Sika and Fosroc as an authorised distributor and applicator across Delhi NCR and Pan-India, so the choice can follow the project specification rather than availability.

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